1. Field of the Invention
The invention relates to a motor vehicle lock with a latch and a ratchet arrangement.
2. Description of Related Art
Current motor vehicle locks are generally equipped with a latch and a ratchet, in order to accomplish a non-positive connection to a striker which is located on the motor vehicle body as shown in EP 0 589 158 A1. The latch can be swivelled around a swivelling axis and, in any case, can be moved into a main locked position. The ratchet is hook-shaped and keeps the latch in the main locked position by fitting into a corresponding shape, i.e., a main catch on the latch. The basic concept is also used in motor vehicle locks with a motorized opening drive, as is also shown in EP 0 589 158 A1.
Basically, in the above-described motor vehicle lock, a problem arises in which, depending on the configuration of the latch and the ratchet, the lifting of the ratchet and thus the release of the latch are associated with a certain minimum force and a certain minimum work which are determined essentially by the friction force between the latch and the ratchet, while the ratchet is being lifted. In addition to the coefficient of friction, for the work consumed by friction, the reset force acting on the ratchet from the latch, and the adjustment path necessary for lifting the ratchet are decisive.
While maintaining the described basic concept, a reduction of the friction force and the work consumed by friction is possible only to a limited degree without endangering the operating reliability of the motor vehicle lock. This leads to possible adverse effects with regard to ease of operation due to high actuating forces in a mechanically actuated motor vehicle lock. When the motor vehicle lock is equipped with a motorized opening drive, the opening drive can be designed accordingly for high forces or powers. However, this leads to high space requirements and to high costs.
One approach to reduce the force necessary for lifting the ratchet is shown by a known motor vehicle lock described in DE 102 36 282 A1 which shows a ratchet arrangement consisting of two ratchets. The first ratchet can be caused to engage the latch in order to keep the latch in the main locked position. The second ratchet can be caused to engage the first ratchet in order to keep in its holding position. The first ratchet is loaded in the direction of its holding position with a spring, which is overdimensioned for this purpose.
The disadvantage in this motor vehicle lock is that the motion of the ratchets must be matched very exactly to one another so that the motor vehicle door does not swing back when closing, caused by overly slow motion of the first ratchet. The matching of the ratchets to one another makes the structure of the motor vehicle lock complex and takes place by means of a spring with high stiffness. This however leads to the actuating forces for lifting the ratchet being increased. The force which is necessary for lifting the ratchet is reduced by the reduction of the friction force, but this reduction is again neutralized at least partially by the high stiffness of the springs.
Another approach to reducing the force necessary to lift the ratchet is shown by the known motor vehicle lock described in EP 0 406 777 B1 corresponds to U.S. Pat. No. 5,092,639, which underlies this invention. Here, a ratchet arrangement which, like the above described ratchet, can be caused to engage the latch in order to keep the latch in the main locked position. The ratchet arrangement consists of a first lever to which a second lever is coupled with a swivelling capacity. The engagement necessary to hold the latch between the ratchet arrangement on one hand, and the latch on the other, takes place via the second lever. To release the latch, the first lever is swivelled which leads to swivelling of the second lever relative to the first lever. At the same time, the second lever rolls off the latch, to a certain extent, until an unstable state is formed, and the latch swivels into its open position. The work consumed by friction can be largely avoided by the swivelling of the second lever when the latch is released.
The problem in this motor vehicle lock resides in the fact that the operating reliability, when the latch is in the main locked position, cannot be adequately ensured. At high external accelerations, the second lever can swivel and lead to unwanted release of the latch. In order to achieve high operating reliability, high pretensioning of the second lever against the first lever would be necessary, which can lead to a high force which is necessary to release the latch.